Known optical switches are designed to rapidly switch optical signals, e.g., in so-called add-drop multiplexers. These add-drop multiplexers are parts of digital transmission systems which operate according to the synchronous digital hierachy (SDH) and in which additional signals are inserted into or branched from a frame-structured time-division multiplex signal.
Such a switch is known from the journal "Electronics Letters", 17th March 1988, Vol. 24, No. 6, pages 340-341 . It comprises a Mach-Zehnder interferometer with two arms. An optical signal is coupled through a first coupler into both arms and is then recombined in a second coupler. An optical switching pulse can be applied to one of the two arms, so that as a result of the Kerr effect, a controlled change in the optical length of this arm occurs for light of a yen direction of polarization. This change causes a phase shift of the two signals. By interference influenced by a controlled phase shift, the optical signal wave in the second coupler is switched. From the journal "Electronics Letters", Apr. 25, 1991, Vol. 27, No. 9, pages 704-705, another optical switch is known which is designed as an interferometer and in which an optical signal wave can be switched by an optical switching pulse. The interferometer used was a so-called Sagnac interferometer.
In both known types of optical switches, a polarized optical signal wave is switched. To obtain a defined interaction between the optical signal wave and the optical switching pulse, the known interferometers include polarization controllers, which, if operated for prolonged periods of time, have to be readjusted due to temperature variations and other influences.
Furthermore, the signal waves frequently come from different signal sources and have different directions of polarization. In that case, too, constant readjustment of the polarization controllers is necessary to permit optimum switching.